Perlite is a glassy volcanic aluminium silicate, containing 2 to 5% combined water, that expands 10-30 times its original volume when heated at temperatures between 760-1150° C. depending on the composition of the raw material. The volatilisation of the combined water during heat treatment expands the hot, softened ore into a foam that solidifies into a lightweight, cellular aggregate with bulk densities ranging between 80-240 kg/m3. The resultant expanded product finds a variety of industrial and construction related applications owing to its main features of: lightweight, porosity, non-flammability, thermal insulation, noise control, anti-sweating and non-toxicity.
Pumice is a lightweight volcanic aluminium silicate with sponge like structure formed by expansion of gases while molten lava rapidly cooled. The name applies to a group of materials having similar origin and physical structure, such as pumicite, volcanic cinders, scoria, and volcanic tuff. It is always associated with recent volcanic activity and it may show acidic and basic properties depending on its SiO2 and CaO/MgO contents with the pumice being more acidic and the cinders, scoria, and tuff being more basic. Pumice has a low bulk density ranging from 480-960 kg/m3, a high strength to weight ratio, low thermal conductivity and low sound transmission characteristics. All these features make it desirable for use as a building material for lightweight block and concrete, an abrasive, an absorbent, a carrier for insecticides and as a mineral filler and conditioner.
Expanded perlite, pumice and pumice related group of materials, exfoliated vermiculite and phlogopite, expanded clays etc. are porous, lightweight and insulative materials which are widely consumed for building-related uses consisting of concrete aggregate, plaster aggregate, formed products and masonry and cavity fill. In the preparation of lightweight and insulative products from these materials; cement, plaster, alkali silicates (water glass) and polymeric materials of various kinds are used as binding agents. Also, fibers of organic and inorganic origin are used for reinforcing purposes in some formulations.
The products obtained suffer from disadvantages such as low resistance to water and fire, lower insulation and compressive strength values depending on the type and the quantity of the binding agent used. For example, when cement or plaster is used, the compressive strength of the formed products increase with increase of the quantity of the cement or plaster used but, corresponding disadvantages in terms of lightness and insulative properties are observed.
It would be preferable, however, to be able to bind such lightweight and insulative materials with minor amounts of binding agent such that the product obtained should be better in terms of mechanical strength, lightness, insulative properties, fire resistance and water insolubility compared to the products being already prepared therefrom.
U.S. Pat. No. 4,451,294 discloses a composition of silicate material in the form of blocks and articles consisting essentially of liquid sodium silicate, solid sodium silicate, borax and perlite. This water resistant, heat insulating (λ=0.04-0.1 W/m·deg.) material possesses a bulk density of from 100 to 300 kg/m3 with a compressive strength of from 0.3 to 1 MPa and can be applied at temperatures of from −50 up to 550° C. Although water resistant, heat insulation and low bulk density characteristics of this composition are in favor, uppermost application temperature being low (550° C.) and especially maximum compressive strength value being only 1 MPa limits its use for many construction related purposes. Also, the major components of the composition are liquid and solid sodium silicates, perlite being used only from 6 to 17% as an additive.
U.S. Pat. No. 4,313,997 discloses a composition comprising 65-95% by weight of perlite and 5-35% by weight of an aqueous emulsified, tacky, polyacrylate resin. Although the amount of expanded perlite in the formulation is high, the product is suitable for use only as a board-like product because of low mechanical and low flame retardancy characteristics.